1. Field of the Invention
The invention relates to an apparatus for shaking sample containers.
2. Description of Related Art
Traditionally, generic apparatus are referred to as vortex mixers. Such mixers can be used for shaking a sample container, and in particular a test tube or centrifuge glass tube for example, which is normally held at its upper end by the operator.
Generic apparatus comprise a drive which is able to move a holder provided on the upper side of the mixer at high frequencies, for example on a narrow circular path or another path that is suitable for mixing.
The holder is designed such that the traditional sample containers, such as test tubes or centrifuge glass tubes, can, with their closed lower end, be arranged therein or thereon in such a manner that the movement of the holder is transmitted to the container.
Generic assemblies are, in particular, used in microbiological laboratories or cell laboratories. A frequent application is the resuspension of pelletized cells, which is only one example. Particularly in this case, the vortex developing in the vessel during mixing ensures that the pellets which can, otherwise, be detached from the wall with difficulty only can be brought in solution again. However, it is also possible to contemplate other applications where it is intended to dissolve solid components or to mix fluids with one another.
To facilitate operation, traditional apparatus provide that the mixing process starts automatically as soon as a sample container, for example a test tube or a centrifuge glass tube, is arranged at a defined position in the holder.
To achieve this, some apparatus comprise on their upper side an optical sensor which detects the presence of, for example, a test tube in the holder and then automatically generates a start signal for the drive. Other apparatus provide a pressure sensor. In this case, the holder must be pressed down by the vessel to be shaken, wherein a start signal is triggered for the drive once the container or the holder pressurized by this container is in a defined position. Accordingly, a stop signal is generated once, in the former case, the test tube is removed out of the range of the optical sensor or, in the latter case, once the holder is unloaded, wherein the mixing process stops instantly in generic apparatus.
Known sensor-controlled assemblies are disadvantageous in that the mixing process is, in an undesired manner, interrupted even if, for example, the sample container is repositioned in the holder or the vessels to be mixed are exchanged.